<Someone> reported that if you polymorph into a flying monster while in a
pit, you must take u.utrap turns to first climb out before you can fly. Of
course, once you're out, you can swoop down into the pit to pick things up
w/o delay. Rather that have you automatically fly out (e.g. like quaffing
a potion of levitation), I thought it was better to take a turn to fly out,
so that's what I've implemented.
The code to deal with exiting a pit is moved to a new climb_pit function
and the "up" command now lets you climb from a pit too (something I've
found non-intuitive in the past).
Finally, I noticed that non-moving monsters could still go up/down even
though they couldn't move around. Added non-moving checks in doup/dodown.
c90746c670